Did you put him in a QT when you bought him? This is a must to protect your main tank. I see this all the time but no one ever does. Do you have a QT? If not go get one to protect your main tank, any fish you buy should be put through quarintine for three weeks before introducing into your main tank also your main tank should set fish free for three weeks or even four to make sure alll the ich you introduced is dead with out a host it will die off.
[hr]
Bill